John a



(No Model.)

J. A. BARRETT.

ANNUNOIATOR AND SHUNT CIRCUIT THEREFOR. No. 360,266. Patented Mar. 29, 1887.

NITED STATES J OHN A. BARRETT, OF BROOKLYN, NEW YORK.

ANNUNCIATOR AND SHUNT-CIRCUIT THEREFOR.

SPECIFICATION forming part of Letters Patent No. 360,266, dated March 29, 1887.

Serial No. 220,913. (No model.)

To all whom it may concern.-

Be it known that I, JOHN A. BARRETT, of Brooklyn, in the county of Kings and State of New Yorlghave invented certain Improvements in Annunciators and Shunt-Circuits therefor, of which the following is a specifica tion.

Hy invention relates to electromagnetic annunciators of the class chiefly utilized as callreceiving appliances for telephone circuits; and its prime objects are to diminish the resistance offered by the helices of such annunciators to the passage of the rapidly-varying telephonic currents, and to provide a shunt or derived circuit round the said helices,whereby not only is an alternative path for the telephonic currents furnished, but in addition to this a short circuit is constituted, wherein the counter-currents developed by the reactions of the electro-magnet upon its surrounding coils may circulate, these being thereby prevented from circulating in the line or main circuit, where otherwise they would materially op pose the legitimate telephonic impulses.

In telephony it has been found that when eleetro-magnets are included in the circuit the telephonic currents are opposed and rendered sluggish and comparatively inefficient to a greater degree than can possibly be due to the mere electrical resistance of the circuit and the instrument-helices, and it has further been demonstrated that this ineflieiency is due to a partial neutralization effected by counter-currents generated in the several electromagnetic helices under the influence of the magnetic variations of the iron cores thereof, which variations are primarily caused by the passage through the said helices of the constantly-varying voicecurrents which traverse the main circuit. Even in comparatively short telephone-lines this adverse influence is clearly perceptible, and its ultimate effect is to diminish the strength and volume of the legitimate or voice currents. When, however, the telephone-1ines are of great length, (as, for example, when the local lines of two central stations at a distance from one another are united by trunk or interurban lines,) the opposing currents due to the magnetic reaction exercise a greatly-intensified influence upon the line, and render the main current so sluggish as to diminish very seriously the distinctness of the reproduced articulate sounds, and to run the words very much together; and inasmuch as it is essential in the operation of long tele phone lines that they shall be disconnected as soon as possible after the discontinuance of a conversation, it is not practicable to dispense with the use of intervening annunciator-magnets, which are required to give a disconnect ing-signal.

By the use of my invention these evils are materially ameliorated; and to this end it consists in establishing a temporary derived or shunt circuit around the electromagnetic helix of the annunciator, which derived circuit shall be of or include a sufficient electrical resistance to allow an adequate amount of the current to pass through the magnet-helix (when a call-signal is transmitted) to excite the core and to attract the working-armature thereof. I also arrange the mechanical details of the shuntcircuit in such a way that the first movement of the said armature operates to break or open the derived circuit, and thus to permit the entire electric signaling-current to pass through the annunciator-helix, which thereupon effects the release of the signaling drop shield or shutter, giving the disconnecting or other signal.

In the drawings which form a part of this specification, Figure 1 is a perspective view of one type of annunciator fitted with the shunting device, and Fig. 3 is a similar perspective view of a modification. Fig. 2 is a diagram of the electrical connections of the type shown in Fig. 1. Fig. 4 is a diagram of the connections of the annunciator shown in Fig. 3; and Fig. 5, a diagram of an electric circuit, including at one station a call-sending and at the other a call-receiving device, illustrating the operation of my invention. Fig. 6 is a diagram illustration of one of the advantages attained by my invention.

Considering, first, Figs. 1 and 2, the main elements of the annunciator are the electromagnet 2 and armature 11, both mounted upon a metal frame or base work, 1. The electromagnet is single, and has operative core polepieces 6 and 7, one at each end. The armature 11 is of soft iron, and is mounted, as hereinafter to be explained, upon an insulating-block carried by a bar pivoted by a screw, 5, in lugs .4, projecting from the rear of one side of the frame. At the free end of this bar is a pawl or detent, which projects through a slot, 10, in the front of the frame, and-which, when the armature is at rest and unattracted, engages with the upwardly-projecting lug Z of the drop or shutter 9, which is hung on pivot-screw p, but which, when the armature is attracted, is withdrawn from the drop, allowing the same to fall. It is to be observed that the armature 11 does not control the drop directly, but through the instrumentality ot' a mechanical connection with the bar 3. The insulatingblock 14 is rigidly affixed to the inner side of the bar 3 near its pivoted point, and a flat spring, 12, is afiixed thereto, which carries the armature l1. Contact-points a and c are placed between the free ends of the armaturell and the bar 3, and the spring 12 is so adjusted that these points are normally in contact with one another. A small bracket, 20, is affixed to the bar 3, and this passes under the armature and terminates on the other side thereof in an upwardly-projecting lug, 19. Through the lug 19 an adjustable screw, 18, of non-conducting material, projects, and by means ofv this screw the distance which the armature can separate from the bar 3 can be regulated, and it also provides means whereby the armature can cause the bar 3 to participate in its motion. Being flexibly attached to the bar 3, the armature is capable of a slight degree of independent motion when attracted by the eleetro-magnet, and, in fact,when the magnet is excited by the passage of a calling-current the armature is attracted and moves toward the cores 6 and 7 and away from the bar 3; but as soon as the armature reaches the nonconducting screw 18 it is enabled, by pressing against the said screw, tocarry the bar 3 with it during the remainder of its path, the distance between the armature and bar being, however, preserved, and the points a and a being thus kept apart.

A derived circuit, including a resistancecoil, 13, is connected in multiple are with the magnet-coil and passes through the points a and a, so that when the apparatus is not being used as a call-signal the points are in contact, and the derived circuit is maintained intact.

It will be understood that the currents used in two binding-screws 16 and 17 are terminals Passing inward, the circuit di vides at the point 29, the main branch leading through wire gto the electro-magnet 2, through the magnet-coils, and out by wire 71, then reaching the junction-point 30, and passing by wire I) to the outgoing-line binding-screw 17. The derived-eircuit branch from point 29 leads by wire 6, spring 12, armature 11, contactpoints a'and a, bar 3, wire 31, resistance-coil 13, and wire (I to junction-point30, and thence out by the wire band binding-screw 17. The wire of the resistance-coil 13 is, in a manner Well understood, wound differentially, to pre vent self-induction. The resistance of the shunt or derived-circuit resistance-coil may be varied within limits of considerable width,

according to the degree of sensitiveness with which the mechanical parts move, and I have found it advisable to use resistances of from one-fourth to one-half that of the magnet-coil.

By the use of this shunted annunciator it will be seen, first, that the electrical resistance between the binding-screws is duringthe transmission of speech diminished in accordance with the law of joint resistances; second, that the voice-currents have an alternative and nonmagnetic route between the said bindingscrews; and, third, that, as indicated 'in the diagram, Fig. 6, the magneto-electric countercurrents developed in the magnet-helix, and represented by the small arrows, have a short circuit provided for them to circulate in, consisting of the electro-magnet, its circuit E, and the derived circuit F, united at their junction-points 29 and 30, and that therefore but an infinitesimal portion of such currents can find their way past thejunction-points to 0ppose the voice-currents (represented by the large arrows) in the main line D O.

In Fig. 5 one of my improved annunciators, A, is represented as being included in the circuit of a main line, which also includes a magneto calling-generator, B.

Figs. 3 and 4 represent a modification, in which, instead of mounting a single armature by a spring on a pivoted bar and thus actuating a circuit-controller in the derived circuit, I provide two independent armatures, both attracted by the same two pole-pieces, 6 and 7, of the two ends of the electro-magnet. One of these, 3, is mounted upon one side of the electro-magnet, and, extending through the slot 10, terminates ina pawl, 8, which controls the shutter or signal-drop. The other, 23, is affixed byfia spring, 21, to an insulating-block, and normally rests against a contact-screw, 24, and the armature 23, together with the contact-screw 24, the wire f, the spring 21, the resistance-coil13, and the connecting-wires i and j, constitute in this case the derived circuit,

which, by the first motion of the armature 23, (this being adjusted more delicately than the armature 3,) is opened at the point of contact between the screw 24 and the armature 23.

I am aware that it is not new, broadly, to construct a shunt-circuit around an electromagnet to prevent the detrimental results of magneto-electrical counter-currents, and that it is not broadly new to provide means, operated by the magnet itself under certain conditions, whereby the derived circuit can be automatically broken. I do not, therefore, broadly claim such an organization; but

I claim- 1. The combination, in an annunciator, of

.an eleotro-niagnet, an armature, a detent-bar adapted to release the visual signal when actuated by said armature, and a shunt or de rived circuit arranged in multiple arc with the annunciator-helix andincluding a contact controlled by said armature, whereby the shunt or derived circuit is broken when the armature is attracted by the magnet, substantially as described.

2. An annunciator for telephone-lines, comprising an electromagnet, a spring-mounted armature therefor, a detent lever or bar adapted to engage the visual signal-drop, mechanically controlled by the armature and normally in electrical contact therewith at one point only,

and a derived circuit, including a suitable re-- sistance normally closed through the point of contact between the armature and detent-bar and shunting the electro-magnet, but adapted to be opened at the said point when the electromagnet is sufficiently excited to attract its armature, whereby the said electro-magnet is shunted during the transmission of speech, and whereby the shunt is broken during the transmission of signals, substantially as described.

3. The combination, in a telephone-line annunciator, of the electro-magnet, the armature attached by a spring to a fixed point, and the detentbar pivoted to a fixed point and provided with a bracket near its free end, within which the armature is adapted to travel, the said bracket being provided with a limit-screw, against which the said armature is adapted to strike before its stroke is completed, whereby the said armature is enabled to traverse a por tion of its stroke before influencing the detent to actuate the signal, substantially as described.

4. Ina telephonic call-annunciator, the combination, substantially as hereinbefore described, of an electro-magnet, a shunt or derived circuit normally closed around the same, an armature for the said electro-magnet, a signal-drop or shutter, a detent-bar controlling the said shutter, the said bar normally being in electrical contact with the armature and forming a part of the derived circuit or shunt, and constituting also a circuit-breaker thereof, and a bracket attached to the side of the detent-bar, and serving as a mechanical link between the said bar and the armature when attracted, whereby the said armature, when actuated by the electro-magnet, is adapted, first, to disrupt the shunt-circuit and thus to re-enforce the elcctro-magnet, and then to engage the said bracket, causing the detent-arni to participate in its movement, and to release the signal-drop and to give thesignal, as specified.

In testimony whereof I have signed my name to this specification,in the presence of two subscribing witnesses, this 3d day of December, 1886.

JOHN A. BARRETT.

Witnesses:

F. H. WVORTMANN, HENRY WV. LoHMEYER. 

